Implantable electrode



Oct. 15, 1968 N. R. HAGFORS IMPLANTABLE ELECTRODE Filed Oct. 20, 1 9 66ATToRNEYJ United States Patent 3,405,715 IMPLANTABLE ELECTRODE Norman R.Hagfors, Minneapolis, Minn., assignor to Medtronic, Inc., Minneapolis,Minn., a corporation of Minnesota Filed Oct. 20, 1966, Ser. No. 588,0156 Claims. (Cl. 128-418) ABSTRACT OF THE DISCLOSURE Electrode apparatusfor stimulating an animal nerve, there being at least three electrodes,one of which is disposed betwen the other two, and the electricalconnection being such that the two outside electrodes are in currentguarding relation to the inner electrode, all to prevent stray currentfrom stimulating adjacent nerves. The electrodes are embedded in asubstance substantially inert to body fluids and tissue.

This invention relates to medical apparatus, and more particularly to animproved implantable electrode for electrical stimulation of a nervewithin the body of an animal. The word animal is here used in its broadsense, including Homo swpiens.

The need for the apparatus of this invention is apparent uponconsideration of such modern medical equipment as the carotid sinusnerve stimulator fully described in a co-pending application by SeymourI. Schwartz and Robert C. Wingrove, Ser. No. 397,899, entitled,Implantable Stimulator tor Reducing Blood Pressure in HypertensivePersons. In this co-pending application there is described the use of animplantable, artificial nerve stimulator, which provides electricalimpulses for stimulation of the carotid sinus nerve to alleviate theproblems of hypertensive animals.

An example of an implantable electrode is fully described in anotherco-pending application by Seymour I. Schwartz, Robert C. Wingrove andJames A. Anderson, Ser. No. 512,981, entitled Implantable Electrode forNerve Stimulation. This last named application describes the use of apair of electrodes, suitable for implantation in the body of an animal.The electrodes are each formed to be connected to spaced points along anerve, to provide electrical stimulation of the nerve from a source ofsignal energy to which the electrodes are connected by flexible leads.The electrodes and leads are made of an electrically conductive materialinert to body fluids and tissues, and are encapsulated, except for theportion of the electrode surrounding the nerve, in another substancewhich is also inert to body fluids and tissue, as well as an electricalinsulator.

One disadvantage of the above described two-electrode configuration isthe limitation of maximum signal pulse which can be applied to theelectrodes to stimulate the nerve. This maximum limitation is caused bystray currents which flow between the electrodes through body fluids andtissue, rather than through the nerve itself. If the stray currentsreach a high enough level, adjacent nerves may be inadvertentlystimulated. The apparatus of this invention overcomes this limitation byproviding an electrode configuration which greatly eliminates straycurrents by providing a plurality of electrically guarding electrodesplaced around an electrically active electrode.

Briefly described, the apparatus of this invention com- 3,405,715Patented Oct. 15, 1968 'ice prises the use of guarding electrodes aroundan active electrode, all of which are connected to or around the desirednerve. In the specific embodiment to be described herein, athree-electrode configuration is used. Two of the electrodes areconnected to a single electrical lead, and the third electrode isconnected to another electrical lead. The electrical leads are connectedto a source of signal energy such that the third electrode is the activeelectrode. The leads in the electrodes are placed in a specially formedencapsulating material substantially inert to body fluid and tissue, andthe leads and electrodes themselves are made of material substantiallyinert to body fluids and tissue. A portion of each of the threeelectrodes is left unencapsulated, to be connected directly to thedesired nerve itself. These portions of each electrode are connected toa nerve in spaced relation, such that the third or active electrode isplaced between the other two electrodes. Therefore, current flowing ineither direction from the active electrode will pass through the nerveto the guard electrodes, rather than pass through body fluids or tissuesurrounding the electrode apparatus.

In the drawings:

FIGURE 1 is a view of an embodiment of this invention which can be usedwith an implantable source of electrical signal energy;

FIGURE 2 is a side view of the embodiment of FIG- URE 1 showing the headof the embodiment having a slot forming an upper and lower layer;

FIGURE 3 is a sectional view of FIGURE 2, taken along the line 33;

FIGURE 4 is a perspective view of the head portion of the embodiment ofFIGURE 1; and

FIGURE 5 is a sectional view of the embodiment of FIGURE 1 taken alongthe line 55, showing the embodiment connected to a nerve and implantedin the body of an animal.

FIGURE 1 discloses an embodiment of this invention having a headindicated generally at 12, a tail 14 connected to head 12 and alsoconnected to a source of electrical signal energy 11.

FIGURE 2 is a side view of head 12 disclosing a slot 21 in head 12forming an upper layer 15 and a lower layer 13. A groove 20 is shown inlower layer 13.

FIGURE 3 discloses a plurality of electrodes 22, 23 and 24, partiallyencapsulated in the substance of lower layer 13, and partially formed togroove 20. A pair of leads 26 and 28, here shown as coiled lengths of anelectrically conductive material, are encapsulated in the substance oftail 14 and head 12. Lead 26 is connected to electrode 22, while lead 28is connected to electrodes 23 and 24.

FIGURE 4 is a perspective view which discloses electrodes 22, 23 and 24connected to spaced points along the length of a nerve or nerve fiber27, such as the carotid sinus nerve.

FIGURE 5 again shows nerve 27 within groove 20 with upper layer 15fastened to lower layer 13 by sutures 29. Head 12 is shown in FIGURE 5as being implanted in the body 30 of an animal.

Because this invention comprises a plurality of electrodes which are tobe implanted within the body of an animal, it is necessary that thesubstance which comprises head 12 and tail 14 be inert to body fluidsand tissue. Such a substance which has been successfully used is siliconrubber. It is also necessary that electrodes 22, 23 and 24, which mustconnect direct-1y to the outer wall of a nerve or nerve fiber 27, be ofa material inert to body fluids and tissue and not be harmful to theouter wall of the nerve to which they are attached. Such a materialwhich has been successfully used is platinum. Another material which mayalso be used is stainless steel. It should be noted that all mention ofmaterials herein are merely exemplary and not intended to so limit thescope of this invention.

As stated above, leads 26 and 28 must also be of material inert to bodyfluids and tissue. It is desirable, but is not mandatory, that leads 26and 28 be of the same material as electrodes 22, 23 and 24.

The leads in the embodiment described herein are disclosed as beingcoiled lengths of a material, to facilitate ease of flexibility. Thishas proven to be a highly desirable type of lead structure, but it isnot intended that this entire invention be limited to such a leadstructure.

While it is necessary that a portion of electrodes 22, 23 and 24- not beencapsulated in the substance of head 12, so that electrodes may beconnected to nerve 27, it is highly undesirable to leave the electrodescompletely exposed after connection to the nerve. To overcome thisproblem the embodiments of this invention provide upper layer 15. Asshown in FIGURES 2, 4 and 5, upper layer is separated from lower layer13 only by the width of slot 21. When electrodes 22, 23 and 24 have beenconnected to nerve 27, upper layer 15 may be fastened upon them by meanssuch as sutures 29. Groove in member 13 is shaped generally to theconfiguration of nerve 27, and also facilitates firm fastening andinsulation of the connection of the electrode to the nerve.

The source of electrical signal energy 11, shown in FIGURE 1, may be atransistorized blocking oscillator powered by a long-life rechargeablebattery, which provides a pulse at a predetermined frequency to thenerve 27. Though the source 11 is here shown as being implantable, thatis, encapsulated in a substance inert to body fluids and tissue forimplantation in the body of an animal, it is not mandatory that theelectrode apparatus of this invention be used with an implantable sourceof electrical signal energy. Tail 14, including leads 26 and 28, mayextend from within the body to a point external of the body, and beconnected to any one of a number of sources of electrical signal energy.Also, the leads may extend to a circuit implanted in the body butpowered from a source external to the body.

The advantage of the operation of the electrodes of this invention, ingreatly decreasing stray current flow through surrounding body fluids,may best be understood by reference to FIGURE 4, showing the threealigned electrodes 22, 23 and 24. Assume first that electrode 23 werenot present, as is the case in the above described application Ser. No.512,981. Assume also that electrodes 22 and 24 are electricallyconnected such that current flow is from electrode 22 to electrode 24.In that case, when a signal pulse is applied across the electrodes,current will flow from electrode 22 to the left through nerve 27 toelectrode 24 and out through lead 28. However, a certain amount ofcurrent will also flow from electrode 22 to the right, and through thebody fluids and tissue around head 12 and back into the left sideopening of groove 20 to electrode 24. This stray current flow is highlyundesirable, especially because of the possibility of simulatingadjacent nerves.

Looking again at the configuration of FIGURE 4 it can be seen that theguarding of active electrode 22 with the additional electrode 23 willgreatly decrease the stray current flow through body fluids and tissue.Now the current which attempts to flow to the right from electrode 22will prefer to flow through electrode 23 and back through lead 28,rather than continue outside around head 12 to the other side ofelectrode 24.

Lab tests have been conducted upon the electrode apparatus and they havebeen successful in increasing the maximum limitation on signal energyapplied to the electrodes by a factor of approximately 4 or 5. In thelaboratory embodiments successfully tested, silicon rubber was used as asubstance to encapsulate the leads and electrodes. In one embodiment theelectrodes were made of platinum, while the leads were made of coiledlengths of stainless steel.

It is apparent from the foregoing description that the apparatus of thisinvention provides a novel improved structure, in the form of animplantable electrode, for connection of a source of signal energy to anerve for providing artificial stimulation of that nerve by timedelectrical pulses from a source of signal energy.

It is apparent that the particular configuration of the embodimentdescribed above is only that of a preferred embodiment, and that theguarded implantable electrode of this invention is not limited merely tothe specific embodiment described.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. Medical apparatus for implantation into the body of an animalcomprising: first and at least two further electrodes of an electricallyconductive material substantially inert to body fluids and tissue; firstand second leads of said material connected, respectively, to said firstand further electrodes, and adapted to be connected to a source ofelectrical signal energy; a first portion of said first and furtherelectrodes and said first and second leads being encapsulated in anelectrically insulating substance substantially inert to body fluids andtissue; a second portion of said first and further electrodes adapted tobe connected to spaced points along a nerve in the body of an animal,for stimulation of the nerve upon receipt of a signal from the source ofsignal energy; said first electrode connected to be electrically activewith respect to said fur-ther electrodes; and said electrodes mountedsuch that said further electrodes are in current guarding relation tosaid first electrode, to limit stray current flow through body fluidsand tissue.

2. The medical apparatus of claim 1 including: a further member of saidsubstance for fastening over said second portion of said first andfurther electrodes when connected to the nerve.

3. Electrode apparatus implantable in the body of an animal forstimulation of a nerve comprising: a housing of an electricallyinsulating substance substantially inert to a body fluids and tissue,said housing having a head and a tail; a slot in said head dividing apart of said head into an upper layer an a lower layer; a groove in saidlower layer adjacent said slot; a plurality of electrodes of anelectrically conductive material substantially inert to body fluids andtissue, and encased in said head of said housing in spaced relation toone another such that a first of said electrodes lies between others ofsaid electrodes; a portion of each of said electrodes formed to andfitted in said groove, said portions adapted to be connected to spacedpoints on a nerve in the body of an animal; a pair of leads of saidmaterial encased in said tail of said housing; and a first of said pairof leads connected to said first of said electrodes and a second of saidpair of leads connected to said others of said electrodes, forconnecting said electrodes to a source of 'signal energy for stimulatingthe nerve.

4. The electrode apparatus of claim 3 in which said top layer of saidhousing is adapted to be fastened to said lower layer to hold and shieldthe nerve in contact with said pair of electrodes.

5. Electrode apparatus implantable in the body of an animal forstimulation of a nerve comprising: first, second and third electrodes ofan electrically conductive material substantially inert to body fluidsand tissue; said electrodes lying in parallel spaced relation, saidsecond electrode lying between said first and third electrodes; firstand second leads of said material, said first lead connected to saidfirst and third electrodes, said second lead connected to said secondelectrode, for connecting said electrodes to a source of electricalsignal energy; encapsulating means References Cited of an electricallyinsulating substance substantially inert UNITED STATES PATENTS to bodyfluids and tissue encapsulating sa1d electrodes and said leads; and aportion of each of said electrodes being 1,679,245 7/1928 Gaertner128418 X exposed through said encapsulating means for connection 5 3,157181 11/1964 McCarty 128404 to spaced points on a nerv 3,216,424 11/1965Chardack 128-418 6. The apparatus of claim 5 including: a :further in-3,279,468 10/1966 Levme 128410 tegral member of said substance forfastening over said exposed portions of said electrodes after connectionthere- RICHARD GAUDET Prlmary Exammer' of to the nerve. 10 W. E. KAMM,Assistant Examiner.

